Characterization of co-seismic gravity variations of Hualian Ms7.3 earthquake based on continuous gravity station network

Monitoring co-seismic gravity changes through continuous gravity observations is of considerable scientific importance for understanding the surface and underground mass redistribution associated to the earthquake processes. In this study, we analyze continuous gravity data from six stations of the Chinese Continuous Gravity Network in Fujian Province to investigate the co-seismic gravity change characteristics associated with the Hualien Ms 7.3 earthquake. To enhance signal extraction, we apply the short-time Fourier transform (STFT) to the gravity records and compare its performance with that of exponential and step-function fitting methods. The results indicate that the STFT approach yields substantially more accurate co-seismic change signals. When evaluated against a viscoelastic layered half-space model and the spherical dislocation theory, the STFT method improves accuracy by more than 20% relative to the other two fitting methods. Further analysis shows that regional geological conditions, manifested through background noise levels, significantly affect the retrieval of co-seismic signals; however, the application of the STFT method effectively suppresses such regional geological influences, thereby enabling more reliable extraction of the earthquake-induced gravity changes. Overall, our findings demonstrate that gPhone gravimeters provide high precision and stability in the low-frequency range, and that the STFT technique offers a robust tool for precise extraction of co-seismic gravity signals, thereby reinforcing the foundations for optimizing earthquake early warning systems and advancing studies of earthquake source mechanisms.